This invention relates to a process for the preparation of .alpha.-fluorinated anisole compounds by the catalyzed vapor phase reaction of hydrogen fluoride with an .alpha.-chlorinated anisole compound. The .alpha.-fluorinated anisoles, especially .alpha.-,.alpha.-,.alpha.-trifluoroanisoles are useful intermediates for the further preparation of various other chemical products including, for example, dyestuffs and agricultural chemicals.
Various reactions are known wherein a fluorinating agent, such as hydrogen fluoride, is reacted with an organic halide, either in the liquid or vapor phase to replace halogen atoms with fluorine atoms. Such processes may utilize atmospheric or super-atmospheric pressures and may be carried out in the presence of a catalyst. Many of the known fluorination reactions, although suitable for laboratory investigations and experiments, or small scale preparations, are unsuitable for larger scale commercial use for various reasons, such as the low purity of product obtained, low yield of the desired product, and cost of equipment employed. Moreover, a catalyst that exhibits good activity under one set of conditions, such as laboratory conditions, may be too costly for large scale preparations, or may be inefficient or inactive under different conditions.
A wide variety of fluorination catalysts are known and have been used for various fluorination processes. It is known, for example, to employ molybdenum pentachloride as a catalyst in liquid phase fluorination of benzotrichloride compounds to form benzotrifluoride compounds. (U.S. Pat. No. 4,098,832). It is further known to employ fluorinated alumina, such as fluorinated .alpha.-alumina, as a catalyst in the vapor phase fluorination of benzotrichloride compounds to form benzotrifluoride compounds. (U.S. Pat. No. 4,436,942.) However, the efficacy of a particular catalyst is highly specific and may depend on the nature of the reactants, that is, the specific compound to be fluorinated and the particular fluorinating agent employed as well as the condition of the fluorination reaction, such as temperature, pressure, and physical phase of reactants.
The preparation of .alpha.-fluorinated anisoles by reaction of hydrogen fluoride with .alpha.-chlorinated anisoles is known and is described in detail in British Pat. No. 765,527. The process disclosed is the non-catalyzed reaction of hydrogen fluoride and a .alpha.-chlorinated anisole at superatmospheric pressures and at a temperature of about 120.degree. to about 220.degree. Celsius. The reference discloses also that the phenol ethers are known to be sensitive and subject to splitting of the ether bridge, especially in the presence of hydrogen chloride. The patent further notes that it is surprising that .omega.-chlorinated (.alpha.-chlorinated) anisoles, that is to say phenol ethers containing halogen in the .omega.(.alpha.-)-position would withstand treatment with hydrogen fluoride, during which hydrogen chloride is evolved. In view of such disclosure it would not be expected that .alpha.-chlorinated anisoles would be capable of withstanding even more severe conditions, such as vapor phase conditions at temperatures in excess of 300.degree. Celsius in the presence of hydrogen fluoride and evolved hydrogen chloride. The aforementioned British Pat. No. 765,527 further indicates that the antimony catalysts generally used for fluorination reactions are not beneficial and may be dispensed with.
It is an object of this invention to provide an improved process for the preparation of .alpha.-,.alpha.-,.alpha.-trifluoroanisole compounds. It is a further object to provide an improved process for the catalyzed vapor phase fluorination of .alpha.-,.alpha.-,.alpha.-trichloroanisole compounds.